(The Conversation) – A vast network of ocean currents nicknamed the “great global ocean conveyor belt” is slowing down. That’s a problem because this vital system redistributes heat around the world, influencing both temperatures and rainfall.

The Atlantic Meridional Overturning Circulation funnels heat northwards through the Atlantic Ocean and is crucial for controlling climate and marine ecosystems. It’s weaker now than at any other time in the past 1,000 years, and global warming could be to blame. But climate models have struggled to replicate the changes observed to date – until now.

Our modelling suggests the recent weakening of the oceanic circulation can potentially be explained if meltwater from the Greenland ice sheet and Canadian glaciers is taken into account.

Our results show the Atlantic overturning circulation is likely to become a third weaker than it was 70 years ago at 2°C of global warming. This would bring big changes to the climate and ecosystems, including faster warming in the southern hemisphere, harsher winters in Europe, and weakening of the northern hemisphere’s tropical monsoons. Our simulations also show such changes are likely to occur much sooner than others had suspected.

National Oceanography Center: “The Atlantic Meridional Overturning Circulation (AMOC): What Is It and Why Is It So Important?”

Changes in the Atlantic Meridional Overturning Circulation

The Atlantic ocean circulation has been monitored continuously since 2004. But a longer-term view is necessary to assess potential changes and their causes.

There are various ways to work out what was going before these measurements began. One technique is based on sediment analyses. These estimates suggest the Atlantic meridional circulation is the weakest it has been for the past millennium, and about 20% weaker since the middle of the 20th century.

Evidence suggests the Earth has already warmed 1.5ºC since the industrial revolution.

The rate of warming has been nearly four times faster over the Arctic in recent decades.

Meltwater weakens oceanic circulation patterns

High temperatures are melting Arctic sea ice, glaciers and the Greenland ice sheet.

Since 2002, Greenland lost 5,900 billion tonnes (gigatonnes) of ice. To put that into perspective, imagine if the whole state of New South Wales was covered in ice 8 metres thick.

This fresh meltwater flowing into the subarctic ocean is lighter than salty seawater. So less water descends to the ocean depths. This reduces the southward flow of deep and cold waters from the Atlantic. It also weakens the Gulf Stream, which is the main pathway of the northward return flow of warm waters at the surface.

The Gulf Stream is what gives Britain mild winters compared to other places at the same distance from the north pole such as Saint-Pierre and Miquelon in Canada.

Our new research shows meltwater from the Greenland ice sheet and Arctic glaciers in Canada is the missing piece in the climate puzzle.

When we factor this into simulations, using an Earth system model and a high-resolution ocean model, slowing of the oceanic circulation reflects reality.

Our research confirms the Atlantic overturning circulation has been slowing down since the middle of the 20th century. It also offers a glimpse of the future.

Connectivity in the Atlantic Ocean

Our new research also shows the North and South Atlantic oceans are more connected than previously thought.

The weakening of the overturning circulation over the past few decades has obscured the warming effect in the North Atlantic, leading to what’s been termed a “warming hole”.

When oceanic circulation is strong, there is a large transfer of heat to the North Atlantic. But weakening of the oceanic circulation means the surface of the ocean south of Greenland has warmed much less than the rest.

Reduced heat and salt transfer to the North Atlantic has meant more heat and salt accumulated in the South Atlantic. As a result, the temperature and salinity in the South Atlantic increased faster.

Our simulations show changes in the far North Atlantic are felt in the South Atlantic Ocean in less than two decades. This provides new observational evidence of the past century slow-down of the Atlantic overturning circulation.

What does the future hold?

The latest climate projections suggest the Atlantic overturning circulation will weaken by about 30% by 2060. But these estimates do not take into account the meltwater that runs into the subarctic ocean.

The Greenland ice sheet will continue melting over the coming century, possibly raising global sea level by about 10 cm. If this additional meltwater is included in climate projections, the overturning circulation will weaken faster. It could be 30% weaker by 2040. That’s 20 years earlier than initially projected.

Such a rapid decrease in the overturning circulation over coming decades will disrupt climate and ecosystems. Expect harsher winters in Europe, and drier conditions in the northern tropics. The southern hemisphere, including Australia and southern South America, may face warmer and wetter summers.

Our climate has changed dramatically over the past 20 years. More rapid melting of the ice sheets will accelerate further disruption of the climate system.

This means we have even less time to stabilise the climate. So it is imperative that humanity acts to reduce emissions as fast as possible.

Laurie Menviel, Post-doctoral Research Fellow, Climate Change Research Centre, UNSW Sydney and Gabriel Pontes, Post-doctoral Research Fellow, Climate Change Research Centre, UNSW Sydney

This article is republished from The Conversation under a Creative Commons license. Read the original article.

(The Conversation) – The melting of one of North America’s largest icefields has accelerated and could soon reach an irreversible tipping point. That’s the conclusion of new research colleagues and I have published on the Juneau Icefield, which straddles the Alaska-Canada border near the Alaskan capital of Juneau.

In the summer of 2022, I skied across the flat, smooth and white plateau of the icefield, accompanied by other researchers, sliding in the tracks of the person in front of me under a hot sun. From that plateau, around 40 huge, interconnected glaciers descend towards the sea, with hundreds of smaller glaciers on the mountain peaks all around.

Our work, now published in Nature Communications, has shown that Juneau is an example of a climate “feedback” in action: as temperatures are rising, less and less snow is remaining through the summer (technically: the “end-of-summer snowline” is rising). This in turn leads to ice being exposed to sunshine and higher temperatures, which means more melt, less snow, and so on.

Like many Alaskan glaciers, Juneau’s are top-heavy, with lots of ice and snow at high altitudes above the end-of-summer snowline. This previously sustained the glacier tongues lower down. But when the end-of-summer snowline does creep up to the top plateau, then suddenly a large amount of a top-heavy glacier will be newly exposed to melting.

That’s what’s happening now, each summer, and the glaciers are melting much faster than before, causing the icefield to get thinner and thinner and the plateau to get lower and lower. Once a threshold is passed, these feedbacks can accelerate melt and drive a self-perpetuating loss of snow and ice which would continue even if the world were to stop warming.

Ice is melting faster than ever

Using satellites, photos and old piles of rocks, we were able to measure the ice loss across Juneau Icefield from the end of the last “Little Ice Age” (about 250 years ago) to the present day. We saw that the glaciers began shrinking after that cold period ended in about 1770. This ice loss remained constant until about 1979, when it accelerated. It accelerated again in 2010, doubling the previous rate. Glaciers there shrank five times faster between 2015 and 2019 than from 1979 to 1990.

Associated Press Video: “Melting of Alaska’s Juneau icefield accelerates, losing snow nearly 5 times faster than in the 1980s”

Our data shows that as the snow decreases and the summer melt season lengthens, the icefield is darkening. Fresh, white snow is very reflective, and much of that strong solar energy that we experienced in the summer of 2022 is reflected back into space. But the end of summer snowline is rising and is now often occurring right on the plateau of the Juneau Icefield, which means that older snow and glacier ice is being exposed to the sun. These slightly darker surfaces absorb more energy, increasing snow and ice melt.

As the plateau of the icefield thins, ice and snow reserves at higher altitudes are lost, and the surface of the plateau lowers. This will make it increasingly hard for the icefield to ever stabilise or even recover. That’s because warmer air at low elevations drives further melt, leading to an irreversible tipping point.

Longer-term data like these are critical to understand how glaciers behave, and the processes and tipping points that exist within individual glaciers. These complex processes make it difficult to predict how a glacier will behave in future.

The world’s hardest jigsaw

We used satellite records to reconstruct how big the glacier was and how it behaved, but this really limits us to the past 50 years. To go back further, we need different methods. To go back 250 years, we mapped the ridges of moraines, which are large piles of debris deposited at the glacier snout, and places where glaciers have scoured and polished the bedrock.

To check and build on our mapping, we spent two weeks on the icefield itself and two weeks in the rainforest below. We camped among the moraine ridges, suspending our food high in the air to keep it safe from bears, shouting to warn off the moose and bears as we bushwhacked through the rainforest, and battling mosquitoes thirsty for our blood.

We used aerial photographs to reconstruct the icefield in the 1940s and 1970s, in the era before readily available satellite imagery. These are high quality photos, but were taken before global positioning systems made it easy to locate exactly where they were taken.

A number also had some minor damage in the intervening years – some Sellotape, a tear, a thumb print. As a result, the individual images had to be stitched together to make a 3D picture of the whole icefield. It was all rather like doing the world’s hardest jigsaw puzzle.

Work like this is crucial as the world’s glaciers are melting fast – all together they are currently losing more mass than the Greenland or Antarctic ice sheets, and thinning rates of these glaciers worldwide has doubled over the past two decades.

Our longer time series shows just how stark this acceleration is. Understanding how and where “feedbacks” are making glaciers melt even faster is essential to make better predictions of future change in this important region

Bethan Davies, Senior Lecturer in Physical Geography, Newcastle University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Dubai’s famous Palm Jumeirah is not the only man-made island to have emerged from the sea this century. Over the past 20 years, many islands have been built to accommodate both tourists and well-heeled residents – especially in the Arabian Gulf states and China.

In an era of sea-level rise and increased storm activity, new islands may seem a risky venture. Yet the desire for a sea view and to put blue water between yourself and the noise, traffic and crime of the mainland is keeping the market buoyant.

Residential artificial islands cater for the rich and have serious environmental consequences. But they ride high on big promises. How else to explain the continuing expansion of Eko Atlantic, a complex of islands sprouting off coastal Lagos in Nigeria?

Digital. “Artificial Islands.” Dream / Dreamland v. 3, 2024.

Construction firms broke ground on Eko Atlantic’s boulevards and high-rise apartments in 2009. The city government has recently announced five more artificial islands “to open up the city”, and claims that the new islands generate and attract wealth and have already created “30,000 direct new jobs”, mostly in construction and maintenance.

The fashion for island-building shows no signs of abating. But instead of an answer to the desperate need for new housing among people who are set to be displaced by rising seas, new islands are offering yet another distraction for the wealthy.

How to build an island

As research for my book The Age of Islands, I visited all sorts of new enclaves that have been reclaimed from the sea. I was amazed at how quickly they can be built. In shallow water, creating an island is not technically complex: usually, the sea bed across a wide area is hoovered up and ground down, then sprayed and pummelled into a stable base.

In Lagos, the Gulf states and other island-building hotspots like the shores of the Chinese island province of Hainan, developers know their creations must be defended from the sea. Nigeria has the Great Wall of Lagos, a sea barrier containing about 100,000 concrete blocks and rising nine metres above the sea, to protect Eko Atlantic. More modest structures are favoured elsewhere, usually in the form of artificial reefs that are dragged and dropped into place, creating a shield against surging seas.

Will any of this be enough? Such barriers provide enough protection long enough to make island-building an economic proposition. But this calculation misses something important: all these islands rely on the mainland – that’s where they get their energy, water and food. Lagos is a low-lying city and large parts are in danger of flooding. The boulevards of Eko Atlantic won’t look so chic if they are marooned.

Critics of new islands point to the havoc they cause to coastal and river systems, changing patterns of sediment deposition and erosion and creating silty, warm lagoons that turn living marine environments into dead zones.

This is one of the reasons the Chinese government intervened to halt island-building around Hainan. From its shores you can see 11 projects, some in full swing, most paused.

The world’s biggest and most spectacular new island, Ocean Flower, is found here. It is shaped like a lotus with scrolling leaves and is already crowded with apartment blocks and outlandish architecture, including European-style castles, grandiose hotels and amusement parks. The plan was to have 28 museums, 58 hotels and the world’s largest conference centre.

Even in the hyperbolic world of island building, it sounds extreme. The developer, Evergrande, is now in financial trouble and 39 residential towers on Ocean Flower have been deemed to have flouted environmental and planning regulations and ordered to be demolished.

Boom-and-bust cycles would appear to plague new islands. But these tales shouldn’t mislead us into thinking this is an ailing industry. The financial incentives remain enormous and island makers are an adaptive breed.

Floating for a few

Floating islands have come to the fore recently: anchored platforms whose construction does not involve scraping away the seabed, making them less disruptive to the marine environment.

Plans for floating cities keep bubbling up. One prospect, Green Float, led by the Japanese company Shimz, would be a floating Pacific city designed to float on the equator “just like a lily pad” and house 40,000 people.

Building on the high seas will always be challenging, so it’s no surprise that ventures closer to shore, such as the Floating City in the Maldives, have been the first to materialise. Floating City is slated as a 500-acre development with 5,000 low-rise homes for 20,000 people arranged in a coral-like scatter of closely connected islets. The first islands have already been towed into place.

The Dutch architect of the scheme, Koen Olthuis, hopes that the Floating City will not be the preserve of the rich (unlike the others I’ve mentioned). His vision is of ordinary Maldivians, having lost homes and livelihoods to rising seas, finding a safe anchorage in the Floating City.

But from what I’ve seen, the world of artificial islands caters to the few not the many. Island-building is led by private developers, not environmentalists – or even states. Foreigners are already being induced to buy into Floating City and told this will be their ticket to a Maldivian residence permit. The bond between wealth and island building will not be easily broken.

Alastair Bonnett, Professor of Geography, Newcastle University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

As much of the Great Lakes region experiences its warmest winter on record, and more record high temperatures are expected in Michigan, the National Oceanic and Atmospheric Administration (NOAA) has reported record low levels of ice coverage on the Great Lakes, amid a steady, decades-long decrease in coverage.

While ice coverage on the Great Lakes usually peaks in the late February to early March, NOAA began reporting daily record-lows for Great Lakes ice coverage on Feb. 8, through Feb. 15. While there was a brief spike above historic lows after Feb. 15, those numbers quickly neared and tied low ice-coverage records, with historical lows recorded on Feb. 27 and 28, Jennifer Day, director of communications for NOAA’s Great Lakes Environmental Research Laboratory said in an email.

Ice coverage on the individual lakes has followed similar patterns, with Lake Superior, Lake Michigan and Lake Huron recording historic low coverage for the date on Feb. 28, while ice concentration for Lake Erie sat at 0% and concentration on Lake Ontario sat at less than half a percent.

NOAA Great Lakes Environmental Research Laboratory Ice Coverage Chart for Feb. 29, 2024. | National Oceanic and Atmospheric Administration.

Ice concentration on Lake Superior sat at 1.74% on Wednesday, while NOAA recorded 3.6% concentration in Lake Michigan and 7.84% concentration in Lake Huron.

The total peak for ice concentration across the five lakes was recorded on Jan. 22, with 16% coverage. However, Lake Superior has since recorded a new maximum for the year on Feb.19, exceeding its January peak.

Ayumi Fujisaki-Manome, an associate researcher at the Cooperative Institute for Great Lakes Research told the Michigan Advance the lack of ice is the result of anomaly conditions overlaid on long term warming trends. Alongside El Niño conditions contributing to a warmer and wetter winter than normal, the North Atlantic Oscillation — which describes atmospheric pressure patterns — is in a positive phase, which prevents cold arctic air from coming down into the Great Lakes region.

Day noted that the strong El Niño coupled with a warm December and above average air and water temperatures throughout winter did not create the conditions needed for ice to develop.

Low ice was also recorded in 2020 and 2023, Day said, with the annual maximum coverage near 20%, compared to the long-term average of 53%.

However, NOAA has also recorded very high ice years in the previous decade, in 2014, 2015 and 2019.

“Even though there’s a decreasing trend in max ice (5%/decade), there is a great deal of year to year variability,” Day said.

Although there has been a long-term decline in Great Lakes Ice Coverage, predicting those fluctuations from year to year remains a big question for researchers, Fujisaki-Manome said.

While a lack of ice may bring disappointment for those looking to ice fish in the Great Lakes, or visit ice caves near the coast, the lack of ice coverage also carries concerns for shoreline conditions, lake effect weather, and for various animal species in and around the Great Lakes.

Ice coverage serves as a barrier, protecting coastlines from high winds, high waves and storm surges. Without that barrier there will be long-term impacts, such as shoreline erosion, Fujisaki-Manome said.

A lack of ice to protect from waves makes shorelines more susceptible to coastal flooding and creates a higher potential for storm damage to shoreline infrastructure, Day said.

Additionally, less ice and more open water is the perfect set up for a lake effect snowstorm or an ice storm, Fujisaki-Manome said.

During late fall and winter cold air flowing over the warm waters of the Great Lakes leads to the production of lake effect snow leading to increased snowfall in areas downwind from the lakes. This effect usually diminishes late into the winter season, as the formation of lake ice reduces the supply of warm and moist air in the atmosphere.

Thick, stable ice also protects fish eggs that are deposited nearshore in the fall and incubate over winter, Day said. Ice cover can help minimize the effect of waves that would dislodge or break apart eggs from species like lake whitefish or lake herring, she said.

Ice cover also affects winter fishery harvests, especially in bays, drowned river mouth lakes and nearshore areas, Day said. During cold winters when ice is thick and lasts three to four months, harvests for panfish, whitefish, bass, walleye and yellow perch are high, with low harvests when coverage is low and unstable.

It is unlikely that total ice coverage across the Great Lakes will exceed its January peak, Day said.

Significant ice growth is not expected over the coming weeks, and longer term temperature trend predictions indicate that ice levels across the Great Lakes will likely remain below average for the next several weeks, Day said.

Kyle Davidson

A heat wave in Greenland and a storm in Antarctica. These kinds of individual weather “events” are increasingly being supercharged by a warming climate. But despite being short-term events they can also have a much longer-term effect on the world’s largest ice sheets, and may even lead to tipping points being crossed in the polar regions.

We have just published research looking at these sudden changes in the ice sheets and how they may impact what we know about sea level rise. One reason this is so important is that the global sea level is predicted to rise by anywhere between 28 cm and 100cm by the year 2100, according to the IPCC. This is a huge range – 70 cm extra sea-level rise would affect many millions more people.

Partly this uncertainty is because we simply don’t know whether we’ll curb our emissions or continue with business as usual. But while possible social and economic changes are at least factored in to the above numbers, the IPCC acknowledges its estimate does not take into account deeply uncertain ice-sheet processes.

Sudden accelerations

The sea is rising for two main reasons. First, the water itself is very slightly expanding as it warms, with this process responsible for about a third of the total expected sea-level rise.

Second, the world’s largest ice sheets in Antarctica and Greenland are melting or sliding into the sea. As the ice sheets and glaciers respond relatively slowly, the sea will also continue to rise for centuries.

Photo by Cassie Matias on Unsplash

Scientists have long known that there is a potential for sudden accelerations in the rate at which ice is lost from Greenland and Antarctica which could cause considerably more sea-level rise: perhaps a metre or more in a century. Once started, this would be impossible to stop.

Although there is a lot of uncertainty over how likely this is, there is some evidence that it happened about 130,000 years ago, the last time global temperatures were anything close to the present day. We cannot discount the risk.

To improve predictions of rises in sea level we therefore need a clearer understanding of the Antarctic and Greenland ice sheets. In particular, we need to review if there are weather or climate changes that we can already identify that might lead to abrupt increases in the speed of mass loss.

Weather can have long-term effects

Our new study, involving an international team of 29 ice-sheet experts and published in the journal Nature Reviews Earth & Environment, reviews evidence gained from observational data, geological records, and computer model simulations.

We found several examples from the past few decades where weather “events” – a single storm, a heatwave – have led to important long-term changes.

The ice sheets are built from millennia of snowfall that gradually compresses and starts to flow towards the ocean. The ice sheets, like any glacier, respond to changes in the atmosphere and the ocean when the ice is in contact with sea water.

These changes could take place over a matter of hours or days or they may be long-term changes from months to years or thousands of years. And processes may interact with each other on different timescales, so that a glacier may gradually thin and weaken but remain stable until an abrupt short-term event pushes it over the edge and it rapidly collapses.

Because of these different timescales, we need to coordinate collecting and using more diverse types of data and knowledge.

Historically, we thought of ice sheets as slow-moving and delayed in their response to climate change. In contrast, our research found that these huge glacial ice masses respond in far quicker and more unexpected ways as the climate warms, similarly to the frequency and intensity of hurricanes and heatwaves responding to changes with the climate.

Ground and satellite observations show that sudden heatwaves and large storms can have long-lasting effects on ice sheets. For example a heatwave in July 2023 meant at one point 67% of the Greenland ice sheet surface was melting, compared with around 20% for average July conditions. In 2022 unusually warm rain fell on the Conger ice shelf in Antarctica, causing it to disappear almost overnight.

These weather-driven events have long “tails”. Ice sheets don’t follow a simple uniform response to climate warming when they melt or slide into the sea. Instead their changes are punctuated by short-term extremes.

For example, brief periods of melting in Greenland can melt far more ice and snow than is replaced the following winter. Or the catastrophic break-up of ice shelves along the Antarctic coast can rapidly unplug much larger amounts of ice from further inland.

Failing to adequately account for this short-term variability might mean we underestimate how much ice will be lost in future.

What happens next

Scientists must prioritise research on ice-sheet variability. This means better ice-sheet and ocean monitoring systems that can capture the effects of short but extreme weather events.

This will come from new satellites as well as field data. We’ll also need better computer models of how ice sheets will respond to climate change. Fortunately there are already some promising global collaborative initiatives.

We don’t know exactly how much the global sea level is going to rise some decades in advance, but understanding more about the ice sheets will help to refine our predictions.

Edward Hanna, Professor of Climate Science and Meteorology, University of Lincoln and Ruth Mottram, Climate Scientist, National Centre for Climate Research, Danish Meteorological Institute

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Superstorms, abrupt climate shifts and New York City frozen in ice. That’s how the blockbuster Hollywood movie “The Day After Tomorrow” depicted an abrupt shutdown of the Atlantic Ocean’s circulation and the catastrophic consequences.

While Hollywood’s vision was over the top, the 2004 movie raised a serious question: If global warming shuts down the Atlantic Meridional Overturning Circulation, which is crucial for carrying heat from the tropics to the northern latitudes, how abrupt and severe would the climate changes be?

Twenty years after the movie’s release, we know a lot more about the Atlantic Ocean’s circulation. Instruments deployed in the ocean starting in 2004 show that the Atlantic Ocean circulation has observably slowed over the past two decades, possibly to its weakest state in almost a millennium. Studies also suggest that the circulation has reached a dangerous tipping point in the past that sent it into a precipitous, unstoppable decline, and that it could hit that tipping point again as the planet warms and glaciers and ice sheets melt.

In a new study using the latest generation of Earth’s climate models, we simulated the flow of fresh water until the ocean circulation reached that tipping point.

The results showed that the circulation could fully shut down within a century of hitting the tipping point, and that it’s headed in that direction. If that happened, average temperatures would drop by several degrees in North America, parts of Asia and Europe, and people would see severe and cascading consequences around the world.

We also discovered a physics-based early warning signal that can alert the world when the Atlantic Ocean circulation is nearing its tipping point.

The ocean’s conveyor belt

Ocean currents are driven by winds, tides and water density differences.

In the Atlantic Ocean circulation, the relatively warm and salty surface water near the equator flows toward Greenland. During its journey it crosses the Caribbean Sea, loops up into the Gulf of Mexico, and then flows along the U.S. East Coast before crossing the Atlantic.

This current, also known as the Gulf Stream, brings heat to Europe. As it flows northward and cools, the water mass becomes heavier. By the time it reaches Greenland, it starts to sink and flow southward. The sinking of water near Greenland pulls water from elsewhere in the Atlantic Ocean and the cycle repeats, like a conveyor belt.

Too much fresh water from melting glaciers and the Greenland ice sheet can dilute the saltiness of the water, preventing it from sinking, and weaken this ocean conveyor belt. A weaker conveyor belt transports less heat northward and also enables less heavy water to reach Greenland, which further weakens the conveyor belt’s strength. Once it reaches the tipping point, it shuts down quickly.

What happens to the climate at the tipping point?

The existence of a tipping point was first noticed in an overly simplified model of the Atlantic Ocean circulation in the early 1960s. Today’s more detailed climate models indicate a continued slowing of the conveyor belt’s strength under climate change. However, an abrupt shutdown of the Atlantic Ocean circulation appeared to be absent in these climate models.

Ted-Ed Video: “How do ocean currents work? – Jennifer Verduin”

This is where our study comes in. We performed an experiment with a detailed climate model to find the tipping point for an abrupt shutdown by slowly increasing the input of fresh water.

We found that once it reaches the tipping point, the conveyor belt shuts down within 100 years. The heat transport toward the north is strongly reduced, leading to abrupt climate shifts.

The result: Dangerous cold in the North

Regions that are influenced by the Gulf Stream receive substantially less heat when the circulation stops. This cools the North American and European continents by a few degrees.

The European climate is much more influenced by the Gulf Stream than other regions. In our experiment, that meant parts of the continent changed at more than 5 degrees Fahrenheit (3 degrees Celsius) per decade – far faster than today’s global warming of about 0.36 F (0.2 C) per decade. We found that parts of Norway would experience temperature drops of more than 36 F (20 C). On the other hand, regions in the Southern Hemisphere would warm by a few degrees.

These temperature changes develop over about 100 years. That might seem like a long time, but on typical climate time scales, it is abrupt.

The conveyor belt shutting down would also affect sea level and precipitation patterns, which can push other ecosystems closer to their tipping points. For example, the Amazon rainforest is vulnerable to declining precipitation. If its forest ecosystem turned to grassland, the transition would release carbon to the atmosphere and result in the loss of a valuable carbon sink, further accelerating climate change.

The Atlantic circulation has slowed significantly in the distant past. During glacial periods when ice sheets that covered large parts of the planet were melting, the influx of fresh water slowed the Atlantic circulation, triggering huge climate fluctuations.

So, when will we see this tipping point?

The big question – when will the Atlantic circulation reach a tipping point – remains unanswered. Observations don’t go back far enough to provide a clear result. While a recent study suggested that the conveyor belt is rapidly approaching its tipping point, possibly within a few years, these statistical analyses made several assumptions that give rise to uncertainty.

Instead, we were able to develop a physics-based and observable early warning signal involving the salinity transport at the southern boundary of the Atlantic Ocean. Once a threshold is reached, the tipping point is likely to follow in one to four decades.

The climate impacts from our study underline the severity of such an abrupt conveyor belt collapse. The temperature, sea level and precipitation changes will severely affect society, and the climate shifts are unstoppable on human time scales.

It might seem counterintuitive to worry about extreme cold as the planet warms, but if the main Atlantic Ocean circulation shuts down from too much meltwater pouring in, that’s the risk ahead.

This article was updated on Feb. 11, 2024, to fix a typo: The experiment found temperatures in parts of Europe changed by more than 5 F per decade.

René van Westen, Postdoctoral Researcher in Climate Physics, Utrecht University; Henk A. Dijkstra, Professor of Physics, Utrecht University, and Michael Kliphuis, Climate Model Specialist, Utrecht University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

(The Conversation) – While the Southern Ocean around Antarctica has been warming for decades, the annual extent of winter sea ice seemed relatively stable – compared to the Arctic. In some areas Antarctic sea ice was even increasing.

That was until 2016, when everything changed. The annual extent of winter sea ice stopped increasing. Now we have had two years of record lows.

In 2018 the international scientific community agreed to produce the first marine ecosystem assessment for the Southern Ocean. We modelled the assessment process on a working group of the Intergovernmental Panel on Climate Change (IPCC). So the resulting “summary for policymakers” being released today is like an IPCC report for the Southern Ocean.

This report can now be used to guide decision-making for the protection and conservation of this vital region and the diversity of life it contains.

Why should we care about sea ice?

Sea ice is to life in the Southern Ocean as soil is to a forest. It is the foundation for Antarctic marine ecosystems.

Less sea ice is a danger to all wildlife – from krill to emperor penguins and whales.

The sea ice zone provides essential food and safe-keeping to young Antarctic krill and small fish, and seeds the expansive growth of phytoplankton in spring, nourishing the entire food web. It is a platform upon which penguins breed, seals rest, and around which whales feed.

The international bodies that manage Antarctica and the Southern Ocean under the Antarctic Treaty System urgently need better information on marine ecosystems. Our report helps fill this gap by systematically identifying options for managers to maximise the resilience of Southern Ocean ecosystems in a changing world.

An open and collaborative process

We sought input from a wide range of people across the entire Southern Ocean science community.

We sought to answer questions about the state of the whole Southern Ocean system – with an eye on the past, present and future.

Our team comprised 205 authors from 19 countries. They authored 24 peer-reviewed papers. We then distilled the findings from these papers into our summmary for policymakers.

We deliberately modelled the multi-disciplinary assessment process on a working group of the IPCC to distill the science into an easy-to-read and concise narrative for politicians and the general public alike. It provides a community assessment of levels of certainty around what we know.

We hope this “sea change” summary sets a new benchmark for translating marine research into policy responses.

So what’s in the report?

Southern Ocean habitats, from the ice at the surface to the bottom of the deep sea, are changing. The warming of the ocean, decline in sea ice, melting of glaciers, collapse of ice shelves, changes in acidity, and direct human activities such as fishing, are all impacting different parts of the ocean and their inhabitants.

These organisms, from microscopic plants to whales, face a changing and challenging future. Important foundation species such as Antarctic krill are likely to decline with consequences for the whole ecosystem.

The assessment stresses climate change is the most significant driver of species and ecosystem change in the Southern Ocean and coastal Antarctica. It calls for urgent action to curb global heating and ocean acidification.

It reveals an urgent need for international investment in sustained, year-round and ocean-wide scientific assessment and observations of the health of the ocean.

We also need to develop better integrated models of how individual changes in species along with human impacts will translate to system-level change in the different food webs, communities and species.

What’s next?

Our report was tabled at an international meeting of the Commission for the Conservation of Antarctic Marine Living Resources in Hobart.

The commission is the international body responsible for the conservation of marine ecosystems in the Southern Ocean, with membership of 26 nations and the European Union.

It is but one of the bodies our new report can assist. Currently assessments of change in habitats, species and food webs in the Southern Ocean are compiled separately for at least ten different international organisations or processes.

The Southern Ocean is a crucial life-support system, not just for Antarctica but for the entire planet. So many other bodies will need the information we produced for decision-making in this critical decade for action on climate, including the IPCC itself.

Beyond the science, the assessment team has delivered important lessons about how coordinated, collaborative and consultative approaches can deliver ecosystem information into policymaking. Our first assessment has taken five years, but this is just the beginning. Now we’re up and running, we can continue to support evidence-based conservation of Southern Ocean ecosystems into the future.

Andrew J Constable, Adviser, Antarctica and Marine Systems, Science & Policy, University of Tasmania and Jess Melbourne-Thomas, Transdisciplinary Researcher & Knowledge Broker, CSIRO

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Featured Image: Courtesy Pat James, Australian Antarctic Division.

The global climate is changing and the Arctic is warming rapidly. These are objectively true statements that most people have come to accept.

But it is also true that Earth’s climate has never been stagnant and climate anomalies have been frequent throughout the past.

How then, do we understand our current situation relative to past climate shifts? Are the impacts of modern climate change comparable to those of the medieval warm period (MWP) or the little ice age (LIA)?

Our recently published study in Anthropocene demonstrates a much more substantial impact to polar bears resulting from recent climate change compared to observations over the last 4,000 years. This suggests that current climatic changes are, indeed, unprecedented in human history.

Ecosystem background

Predators at the top of the food chain, like polar bears, reflect changes across the entire ecosystem, all the way down to microscopic algae.

In the Arctic, the base of the food web is sourced from two categories: sea ice-associated algae and open-water phytoplankton, which are distinguishable through their carbon isotopes.

In our study area — centred on Lancaster Sound in the Canadian Arctic Archipelago — the food web is fed by a combination of both sea ice algae and phytoplankton. We can assess the relative importance of these two sources through the stable isotopes incorporated into the tissues of animals.

The relative abundance of carbon isotopes does not change as they are transferred through the food web, so these isotopes tell us about the carbon sources at the base of the food web. Nitrogen isotopes do change as they are passed up the food chain, which tells us who is eating whom.

Results from our study

In our study we examined stable carbon and nitrogen isotopes in polar bear bone collagen.

The polar bears were all from the Lancaster Sound sub-population and spanned the last 4,000 years. We acquired samples of modern polar bear (1998-2007) obtained through hunting and we were able to compare them to samples from archaeological excavations conducted in the region.

The span of time captured by the archaeological samples was vast, but by dividing them into time bins associated with the cultural traditions in the region we were able to compare the samples across time before present (BP): pre-Dorset (4000-2800 years BP), Dorset (1500-700 BP) and Thule (700-500 BP).

The Dorset/Thule cultural transition occurred at the onset of the medieval warm period, so a comparison of these time bins allows us to look at the state of the food web before and during a known climate shift. The Thule time bin also extends into the beginning of the little ice age giving us a glimpse into that period as well.

What it all means

First, the good news. The results of the nitrogen isotopes showed that throughout time, 4,000 years BP to the present, the structure of the Lancaster Sound food web was relatively unchanged. Polar bears eat seals, seals eat cod, cod eat zooplankton, et cetera. There were no surprising shifts in the diets of polar bears despite past and present climate change. This is comforting.

The results of the carbon isotopes tell a less encouraging story, however. Throughout the four millennia encapsulated by the ancient time bins, we saw stability in the mixture of sea ice algae and open water phytoplankton. We did not detect a difference in the origin of carbon at the base of the food web resulting from the medieval warm period or the little ice age.

The modern samples, however, showed a significant difference in the source of carbon, resulting from a greater proportion of open water phytoplankton and less reliance on sea ice algae.

Evidence of a warming climate

Sea ice is an important habitat in the high Arctic. For polar bears it is a platform for hunting. For ringed seals, the primary prey of polar bears, it is a platform for denning and raising young.

The algae that grows in association with sea ice is also very important for jumpstarting biological productivity before the open water season. Our study shows that the loss of biological productivity associated with sea ice is unprecedented on a very long timescale.

Archaeological materials can provide valuable context to the ongoing climate discussion. Much of the valuable work being undertaken is tracking ecosystem changes on a short timescale, seasons to decades. But as we have demonstrated, the Arctic has already changed, so we should not always assume that we are looking at a pristine or undisturbed state.

Image by Peter Fischer from Pixabay

Adding a lens that looks back into the distant past gives resolution and context to our collective understanding of our situation.

In this case, we have illustrated the magnitude of difference occurring in the modern Arctic, relative to past climate anomalies. The medieval warm period and onset of the little ice age were not visible in the isotopes of the Lancaster Sound food web but modern warming is very apparent. We can, therefore, not dismiss calls to action on climate change on the basis that the climate has always fluctuated.

Jennifer Routledge, PhD Candidate, Environmental and Life Sciences, Trent University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Climate change will wreak havoc on small island developing states in the Pacific and elsewhere. Some will be swamped by rising seas. These communities also face more extreme weather, increasingly acidic oceans, coral bleaching and harm to fisheries. Food supplies, human health and livelihoods are at risk. And it’s clear other countries burning fossil fuels are largely to blame.

Yet island states are resourceful. They are not only adapting to change but also seeking legal advice. The international community has certain legal obligations under the law of the sea. These are rules and customs that divvy up the oceans into maritime zones, while recognising certain freedoms and duties.

So island states are asking whether obligations to address climate change might be contained in the United Nations Convention on the Law of the Sea. This is particularly important as marine issues have not received the attention they deserve within international climate negotiations.

If states do have specific obligations to stop greenhouse gas pollution damaging the marine environment, then legal consequences for breaching these obligations could follow. It is possible small island states could one day be compensated for the damage done.

Why seek an advisory opinion?

The International Tribunal for the Law of the Sea is an independent judicial body established by the UN Convention on the Law of the Sea. The tribunal has jurisdiction over any dispute concerning the interpretation or application of the convention and certain legal questions requested of it. The answers to these questions are known as advisory opinions.

Advisory opinions are not legally binding, they are authoritative statements on legal matters. They provide guidance to states and international organisations about the implementation of international law.

The tribunal has delivered two advisory opinions in the past: on deep seabed mining and illegal, unreported and unregulated fishing activities. These proceedings attracted submissions from states, international organisations and non-governmental organisations such as the World Wide Fund for Nature (WWF).

Late last year, the newly established Commission of Small Island States on Climate Change and International Law submitted a request for advice to the tribunal. It concerns the obligations of states to address climate change, including impacts on the marine environment.

Image by David Mark from Pixabay

The tribunal received more than 50 written submissions from states and organisations offering opinions on how it should respond. These submissions, from Australia and New Zealand among others, were recently made public.

While the convention was not designed as a mechanism for regulating climate change, its mandate is broad enough to consider the connection between climate and the oceans. To establish this, the 40-year-old framework agreement must be interpreted in light of changing global circumstances and changing laws, including obligations to strengthen resilience in the high seas. One avenue to achieve this is through an advisory opinion from the tribunal.

The question before the tribunal

The question to the tribunal asks, what are the specific obligations of states:

(a) to prevent, reduce and control pollution of the marine environment in relation to the deleterious effects that result or are likely to result from climate change, including through ocean warming and sea level rise, and ocean acidification, which are caused by anthropogenic greenhouse gas emissions into the atmosphere?

(b) to protect and preserve the marine environment in relation to climate change impacts, including ocean warming and sea level rise, and ocean acidification?

This question invokes specific language from the convention. That provides clues as to which sections of the treaty the tribunal will refer to in its opinion.

The question refers explicitly to the part of the convention entitled “Protection and Preservation of the Marine Environment”. This part sets out the general obligation of states to protect and preserve the marine environment, as well as measures to “prevent, reduce and control pollution”. It also tells states they must not transfer damage or hazards, or transform one type of pollution into another.

Pollution of the marine environment is defined in the convention as:

the introduction by man, directly or indirectly, of substances or energy into the marine environment, including estuaries, which results or is likely to result in such deleterious effects as harm to living resources and marine life, hazards to human health, hindrance to marine activities, including fishing and other legitimate uses of the sea, impairment of quality for use of sea water and reduction of amenities.

What if states do not meet their obligations?

The tribunal will need to answer a key question for the law of the sea: can the convention be understood as referring to the drivers and effects of climate change? And if so, in what ways does the convention require that they be addressed by states?

What the commission’s question does not ask is, what happens when states do not meet their obligations? The answer is particularly important to small island states, who are dissatisfied with ongoing negotiations on addressing loss and damage associated with climate change impacts.

Obligations relating to climate change are contained within other treaties and rules, including the UN Framework Convention on Climate Change and the Paris Agreement. Small island states have sought advice from different courts to clarify these obligations.

The International Court of Justice will consider a wider set of legal issues on climate obligations next year.

The fact that the court has authorised the commission to participate in this separate advisory opinion request signals the UN’s main judicial body will take account of the tribunal’s opinion. It’s also worth noting the tribunal is likely to deliver its views on the law of the sea first, setting the stage for a broader interpretation of international law when it comes to taking responsibility for polluting the atmosphere.

Sustained pressure from small island states is advancing our understanding of the obligations of states to address climate change.

Ellycia Harrould-Kolieb, Lecturer and Research Fellow in Ocean Governance, University of Melbourne and Postdoctoral Researcher, UEF Law School, University of Eastern Finland, The University of Melbourne and Margaret Young, Professor, The University of Melbourne

This article is republished from The Conversation under a Creative Commons license. Read the original article.